, Salem, MA


October 12, 2013

Auto Scanner: Problem with exhaust smell could have multiple solutions

Q: My 2003 Dodge Dakota four door, four-wheel drive pickup has been emitting an “exhaust” odor both outside the vehicle, as well as in the cab area for about a year. I purchased the truck new and have always followed the vehicle’s scheduled services and made all repairs as necessary. The truck was maintained by the selling dealership almost exclusively until the extended warranty expired about two years ago. I have been bringing the truck to the same local mechanic since then, and he is very familiar with its service history. I have had two shops check out the exhaust system for any leaks or any obvious filter/breather fouling issues without any success. I will provide you with some additional information that I hope will be helpful, as you put your many years of automotive troubleshooting knowledge and problem solving experience to work: no loud exhaust noise; one exhaust flange gasket was replaced two years ago; 99,000 miles; 3.9 liter, six-cylinder engine; automatic transmission; complete tune-up, including new wires 12 months ago. I plan to keep my truck running as long as possible.

A: Great letter with lots of good info! Step one is to smoke the tailpipe and look for leaks. Step two would be to smoke the intake manifold to look for leaks. Finally, and I think this is where you will find your problem, is at the oil fill cap. Your 3.9-liter engine uses an oil fill cap designed like that used on the 4.7-liter engine. It’s a screw-on cap and gasket that wears out after a period of time. If the PCV is not working, excess pressure will build in the crank case and look for a place to escape. If it is leaking out the cap, it will go into your vehicle HVAC system and result in a strong smell inside the cab. If the engine is greasy, I recommend you steam clean the engine before checking for leaks. A thorough examination of the fuel system, including the fuel filler neck and attached parts, should be performed as well.

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